This invention relates to the field of optical elements and devices, and more particularly to graded thickness optical elements.
Conventional optical elements and devices have found widespread use in modern technology for producing, receiving and/or controlling light, for example, in communication systems, laser printers, compact disk players, and so on. For many such applications, a light source such as a semiconductor laser or LED is coupled to a semiconductor receiver (e.g. photodiode) through a fiber optic link, free space, or off a reflective surface.
In some cases, micro mirrors are used to direct light as desired, such as in wavelength division multiplexing, optical filtering, as well as other applications. Micro-mirrors are also commonly used to, for example, create optical cavities, such as Fabry-Perot cavities, for Vertical Cavity Surface Emitting Lasers (VCSEL), Resonant Cavity Photo Detectors (RCPD), and other devices. A limitation of many conventional micro-mirrors is that the reflectance provided by the micro-mirror is uniform across the optical path or cavity. When applied to VCSEL and RCPD devices, for example, such uniform lateral reflectance can favor multi-mode operation. For many applications, however, a single lowest-order mode of operation is desirable. A single lowest-order mode can help couple the light into single-mode fibers, and may also be desirable for free-space and/or wavelength sensitive systems.
Micro-lenses have also found widespread use in many of today""s systems. Micro-lenses are often used for focusing, directing, and/or controlling light in a wide variety of optical applications. For example, micro-lenses can be used to help align optical fibers, such as single mode optical fibers, with other electro-optical elements, such as LEDs, VCSELs, RCPDs, etc. Micro-lenses can also be used in printer, compact disk player, and other applications to considerable advantage.
The present invention provides a graded thickness optical element for use in a wide variety of applications, including those mentioned above and many others. It is contemplated that the graded thickness optical element of the present invention may function as a mirror, a lens or both, depending on the application. In a preferred embodiment, the graded thickness optical element includes one or more layers, each having a thickness that is graded laterally across the optical element. For micro-lens applications, the refractive index of selected layers may be substantially the same. For micro-mirror applications, the refractive index of selected layers may be different from adjacent layers. Methods for forming the graded thickness optical element are also contemplated. In a preferred embodiment, the graded thickness optical element is formed by depositing one or more layers of the optical element through an aperture that is spaced above a receiving substrate, wherein the deposited graded thickness optical element extends laterally beyond the aperture, in at least one region.